The present invention is with respect to solenoid valve units, and more specially to such units designed for the control of the supply of driving air to a compressed air driven system and letting off of such air therefrom, having a pressure supply port, a pressure outlet port, a let off port for the valve space and a further let off port for the said air driven system.
An account of solenoid valve unit on this lines is to be seen in the U.S. patent application Ser. No. 441,333, now abandoned. The invention of this earlier application may be thought of as a further development of such a solenoid valve unit in the form of a 3/2 solenoid valve. To some degree this earlier invention was based on the idea that the solenoid of a solenoid valve may be designed with a smaller size, as is frequently desired, if the valve member moved thereby is more specially used only for the control of the air current that is under a high pressure. In fact for this air current, only a small flow cross section is needed so that the function of overcoming the pressure forces acting on the valve member may be taken care of by a relatively small solenoid. The letting of the large amounts of expanded air from the air driven system or load is on the other hand controlled by a second valve member by which a large-size, further pressure let-off port may be uncovered or opened up. If for example the air driven system is run on an inlet pressure of roughly 6 atm. and the pressure of the air let off therefrom is roughly 1 atm, the flow cross section for the expanded spent air has to be about 5 to 6 times larger than the flow cross section for the air supplied under a high pressure. If the pressure let off port were to have to be opened or shut with a solenoid valve unit, respresentatively larger valve parts with a respresentatively greater inertia would be needed. Furthermore there would be a parallel increase in the amount of power needed for driving such a valve. If on the other hand in keeping with the invention of said earlier U.S. patent application one has a pressure let off port with a large cross section in the valve member, such port being opened and shut by a pressure-driven second valve member, the solenoid valve unit may be kept for the control of the air current under a high pressure, and not put to any other uses. The outcome is that the unit may be made with a respresentatively smaller, cheaper and more simply controlled solenoid.
In keeping with the basic idea of the invention of said earlier U.S. application Ser. No. 441,333, now abandoned, a solenoid valve unit may take the form of a 3/2 solenoid valve with a valve housing that has a pressure port, a power air outlet port to be joined up with the air driven system or load and a first air let off port. Using the solenoid valve unit it is then possible for the load to be acted upon by compressed air from the compressed air supply, in which respect in a first position of switching of the solenoid valve unit power air outlet port is joined up with the pressure port. The connection of the power outlet port pressurewise with the pressure port is in this respect caused by the motion of a valve member, that is placed inside the valve housing and is drivingly joined up with the armature of the said solenoid. The valve member is more specially loaded towards its resting or neutral position. If the solenoid is acted upon by a current pulse of the right size and form, the valve member is moved out of the resting position into a working position. In the first switching position of the valve member a connection is then produced between the pressure port and the power outlet port of the valve housing. Because of this the air driven load is acted upon by the compressed air. If this condition of operation is to be ended, then the solenoid is so worked that the valve member is moved into a second switching position that is adjusted as may be desired. This second position is for shutting off the air connection between the pressure port and the power outlet port. Once this air connection has been shut down, so that the compressed air supply is shut off from the air driven load, it is necessary for air to be let off at a high speed from the solenoid valve unit on the one hand and the air driven load or system on the other. The valve space from which air is to be let off of the solenoid valve unit, with the valve member placed therein, has in this respect a relatively small volume. The air may be let off therefrom by way of an air let off port with only a small flow cross section, said port being able to be opened and shut, as is known, by the magnetically worked valve member itself. The cross section of the let off port may in this respect be so small that it generally hardly makes any difference to the overall size of the solenoid valve unit and more specially of the solenoid. On the other hand for letting off air from the air driven load it is as a rule necessary for large volumes of expanded, low pressure air to be controlled. In the invention of the said earlier application such control is undertaken by a further pressure let off port having a large cross section, that under the control of a second valve member is joined up with the power air port. The second valve member is not magnetically worked but by the pressure of the air at a point downstream from the first valve member. For this reason the second valve member does not have to be taken into account in selecting the size of the solenoid of the valve unit. On balance the outcome is a system with trouble-free let off of air from large air driven systems using very small solenoid valve units needing little driving power and able to be driven directly from electronic circuits.
The said U.S. patent application has an account of a solenoid valve unit in the form of a 3/2 valve, whose operation is based on the idea noted hereinbefore and having all the parts important for its function integrated into a single valve housing. In this respect a generally coaxial line-up of the parts and structures of the valve is used in which the pressure port and the power air port are placed on opposite sides of the valve housing, whereas the further pressure let off port is placed opening at a third surface of the housing that is at a right angle to the other sides of the housing. In this respect the pressure let off port is so placed as to be running from a hole in the housing between the pressure port and the power air port, the said second valve member being kept in place within this hole. This design makes it necessary for the valve housing to be relatively long seeing that the pressure port, the hole therein and the power air port have to be placed one after the other in it in a row. This form of valve housing takes up much space and this is a shortcoming. On the other hand a design is not as desired if three sides of the valve housing of the solenoid valve unit are taken up partly by ports, such design limiting the uses of the solenoid valve unit and being more specially undesired if the solenoid valve unit is to be joined up with others in part of a modular system.